Merck & Co. Inc. (MRK) is set to face hundreds of legal claims for its osteoporosis drug Fosamax (alendronate sodium) after the drug maker allegedly failed to warn about the risks of thigh bone fractures linked to the drug's use in a timely fashion. (See also, Amgen's Osteoporosis Drug Crosses a Hurdle.)

Fosamax is an old, established drug since 1995 which is used to treat or prevent bone loss in post-menopausal women. Merck garnered healthy revenues from drug sales until ts patent expired in 2007. The medicine is now available as a generic drug.

Thigh Fractures Related to Drug Use

The matter pertains to several old cases where plaintiffs claimed to have suffered thigh fractures which they believed were attributed to long-term use of Fosamax. The plaintiffs said that Merck was aware of the risk of fractures, but delayed adding a warning label to the drug by more than a decade.

In a March 2014 verdict, U.S. District Judge Joel Pisano had annulled all claims by plaintiffs who were injured prior to September 14, 2010, saying the “claims were pre-empted.” The verdict left only about 20 active cases.

In the most recent order, the U.S. Circuit Court of Appeals in Philadelphia found that the lower court judge made a mistake in concluding their state law claims were pre-empted by federal law, based on actions of the FDA. The appeals court found that the plaintiffs have offered sufficient proof for a jury to conclude that the Food And Drug Administration (FDA) would have approved "a properly worded warning about the risk of thigh fractures - or at the very least, to conclude that the odds of FDA rejection were less than highly probable," reports Reuters.

The appeals court judge has now allowed the plaintiffs to go ahead with the trial.

Merck is also facing several lawsuits over its shingles drug Zostavax, after patients reported severe side effects and even death. (See also, Merck's Zostavax Drug Hit With Lawsuits.)

Merck stock was trading down by about 0.75% on Wednesday morning following the news.